Drug Interactions

It is a truism to say that those who engage in drug-taking behaviour may not be particularly selective about the drug they consume. If the preferred drug is unavailable, or if they are in a social situation where drugs are being shared, then they may decide to use another drug. For example, someone using methamphetamine may use ecstasy or cocaine if it is available. This results in a form of polypharmacy where different drugs may be consumed at the same or overlapping times. This has the potential for significant interactions between drugs and their effects.

The main form of interaction is when different drugs act to produce similar responses but by slightly different mechanisms. For example, methamphetamine and cocaine, or ecstasy and amphetamine. The resulting risk of adverse effects can be largely predicted by the individual characteristics of the drugs consumed. Combining potent stimulants of the adrenaline/noradrenaline/dopamine axis will produce stronger effects on arousal, aggression, judgement etc. Opiates and alcohol are both central nervous system depressants and their combination enhances the risk of respiratory arrest.

Some drugs are taken together because the effects of one may counter some of the adverse effects of another. For example, benzodiazepines, such as diazepam, may be taken a short time prior to consuming cocaine to blunt the anxiety and psychosis associated with cocaine use. Again, predictable from the known pharmacology of the individual drugs.

However, and the point of this month’s blog, some interactions are less easy to predict, and it is only by the experience of the users that some effects are revealed. A recent report has described a ‘state of emergency’ in New Haven in the USA after at least 76 people presented with signs of overdose, with 25 cases treated by paramedics in a single 3 hour period. It is thought that these overdoses were caused by taking mixtures of synthetic cannabinoids (such as K2) and potent synthetic opioids such as fentanyl, and also other new psychoactive substances (NPS) imported from other countries.

NPS, by definition, are not characterised in terms of their effects, mechanism of action and potential toxicity. In effect, new and emerging compounds are being tested first on human populations. Without an understanding of the properties of these new drugs, users are putting themselves at greater risk of harm. In addition, the risk of combinations of these drugs is completely unknown.

Although reported only in the USA to date, it is a trend that may become more widespread.

In the next blog, I shall report on some of the papers presented at the 2018 TIAFT (The International Association of Forensic Toxicologists). I am currently in the historic town of Ghent, Belgium and with over 700 delegates there is a great opportunity to exchange information and insights about drug and alcohol use, detection and management.